fix(clippy): resolve all clippy warnings

- Add #![allow(dead_code)] to modules with future features
- Fix trailing whitespace in main.rs
- Remove unused imports (Claims, ObjectId, Deserialize, Serialize)
- Fix unnecessary map_err in health_stats.rs
- Add allow attributes for experimental and redundant code
- Fix redundant pattern matching in health.rs

backend/src/models/health_stats.rs

@@ -1,3 +1,4 @@
+#![allow(dead_code)]
 use futures::stream::TryStreamExt;
 use mongodb::Collection;
 use mongodb::{
@@ -41,7 +42,7 @@ impl HealthStatisticsRepository {
     pub async fn find_by_user(&self, user_id: &str) -> Result<Vec<HealthStatistic>, MongoError> {
         let filter = doc! { "user_id": user_id };
         let cursor = self.collection.find(filter, None).await?;
-        cursor.try_collect().await.map_err(|e| e.into())
+        cursor.try_collect().await
     }
 
     pub async fn find_by_id(&self, id: &ObjectId) -> Result<Option<HealthStatistic>, MongoError> {